Equilibria & Le Chatelier

A complete revision set covering reversible reactions, dynamic equilibrium, Le Chatelier’s principle, and the Haber process, written in Edexcel mark-scheme style. Includes short 1-mark definitions (e.g., reversible reaction, catalyst, closed system) and long 2–4 mark explanations (e.g., effects of temperature, pressure, concentration on equilibrium, compromise conditions in the Haber process). Perfect for exam-style revision, with all answers formatted in M1, M2… structure, single-line per card for easy memorisation and self-testing.

Describe how the position of equilibrium changes when the concentration of a reactant is increased

M1 equilibrium shifts to use up the added reactant,

M2 more products are formed,

M3 to oppose the change

Describe how the position of equilibrium changes when the concentration of a product is increased

M1 equilibrium shifts to use up the added product,

M2 more reactants are formed,

M3 to oppose the change

Describe how equilibrium shifts when pressure is increased for a reaction with unequal moles of gas

M1 equilibrium shifts to the side with fewer moles of gas,

M2 reduces pressure,

M3 favours the formation of products or reactants depending on which side has fewer moles

Describe how equilibrium shifts when pressure is decreased for a reaction with unequal moles of gas

M1 equilibrium shifts to the side with more moles of gas,

M2 increases pressure,

M3 favours the formation of products or reactants depending on which side has more moles

Describe how equilibrium shifts when temperature is increased for an exothermic reaction

M1 equilibrium shifts in the endothermic direction, M2 absorbs heat, M3 less product is formed

Describe how equilibrium shifts when temperature is decreased for an exothermic reaction

M1 equilibrium shifts in the exothermic direction,

M2 releases heat,

M3 more product is formed

Describe how equilibrium shifts when temperature is increased for an endothermic reaction

M1 equilibrium shifts in the endothermic direction,

M2 absorbs heat,

M3 more product is formed

Describe how equilibrium shifts when temperature is decreased for an endothermic reaction

M1 equilibrium shifts in the exothermic direction,

M2 releases heat,

M3 less product is formed

Explain the effect of a catalyst on the rate and position of equilibrium

M1 catalyst increases rate of forward and backward reactions equally,

M2 equilibrium position does not change,

M3 equilibrium is reached faster

Describe how the Haber process equilibrium is affected by pressure

M1 higher pressure shifts equilibrium to the side with fewer gas molecules,

M2 increases ammonia yield,

M3 industrially high pressure is used to increase yield

Describe how the Haber process equilibrium is affected by temperature

M1 lower temperature shifts equilibrium in the exothermic direction,

M2 increases ammonia yield,

M3 higher temperature increases rate but reduces yield,

M4 compromise temperature used

Explain why a compromise temperature is used in the Haber process

M1 low temperature gives high yield but slow rate,

M2 high temperature gives fast rate but lower yield,

M3 compromise gives reasonable yield in acceptable time

Explain why a compromise pressure is used in the Haber process

M1 very high pressure gives high yield,

M2 very high pressure is expensive and unsafe,

M3 compromise gives good yield at manageable cost

Explain why the Haber process uses a catalyst

M1 increases rate of reaction,

M2 does not change position of equilibrium,

M3 allows lower temperature to be used without reducing yield

Describe how changing concentration, temperature or pressure can increase yield of a product

M1 change conditions in the direction that favours the desired product,

M2 shifts equilibrium to form more product,

M3 depends on whether reaction is exo/endothermic and gas moles